1. Field of the Invention
This invention relates to wet connection systems for connecting a conductor or conductors to equipment deployed in a borehole, for example, an oil or gas well.
2. Related Art
Wet connection systems known in the art provide a connection that can be made and unmade in-situ in a liquid environment so that the deployed equipment can be disconnected and recovered without removing the conductor from the borehole, and then re-connected to the conductor in situ when the equipment is re-deployed.
Commonly, the or each conductor is an electrical conductor, which may be used for example to provide a data connection or to supply power to a tool or equipment such as an electric submersible pump assembly (ESP). In other applications, the or each conductor may comprise for example a fibre-optic conductor or a tube for conducting pressurised hydraulic fluid to supply power to a tool deployed in the borehole. Usually, an oil or gas well will be lined with tubing that is cemented into the borehole to form a permanent well casing, the inner surface of the tubing defining the wellbore. (In this specification, a “tube” or “tubing” means an elongate, hollow element which is usually but not necessarily of circular cross-section, and the term “tubular” is to be construed accordingly.) The fluid produced from the well is ducted to the surface via production tubing which is usually deployed down the wellbore in jointed sections and (since its deployment is time consuming and expensive) is preferably left in situ for the productive life of the well. Where an ESP is used to pump the well fluid to the surface, it may be permanently mounted at the lower end of the production tubing, but is more preferably deployed by lowering it down inside the production tubing on a wireline or on continuous coiled tubing (CT), so that it can be recovered without disturbing the production tubing.
It is known for example from US 2003/0085815 A1 to provide a well casing with a docking station which is connected to the surface by conductors. The docking station and conductors are deployed together with the casing and permanently cemented into the borehole together with the casing. Tools deployed down the well may be releasably connected to the conductors via the docking station.
WO2005003506 to the present applicant discloses a wet connection system in which one or more conductors are arranged in the annular gap between a string of production tubing and a well casing and terminate at a connection structure fixed to the lower end of the production tubing. An ESP is lowered down the production tubing and connected with the conductors by an arm which moves radially outwardly to engage the connection structure.
In practice, the last mentioned system may be used to deploy an ESP or other equipment by remote control in an oil or gas well by connecting it to a connection structure on the production tubing at a depth of several kilometers in an aggressive environment in which it is subjected to high pressures and temperatures, heavy mechanical loading, vibration, corrosive fluids, dissolved gases which penetrate electrical insulation and particulates which can clog mechanical parts. Since the wet connection between the deployed equipment and the conductors is made and unmade in this environment, failure often occurs in the region of the wet connector assembly and, less frequently, in the conductors which connect it to the surface, and, where the conductors are electrical power conductors, most frequently in the insulation of the electrical conductors close to the point of connection. By unmaking the wet connection and recovering the deployed equipment to the surface, damaged connectors on the deployed equipment can be identified and repaired. However, damaged connectors at the lower end of the conductors can only be inspected and replaced by recovering the entire string of production tubing, which is laborious and expensive.